EP0030664B1 - Poudres à fritter fluides à propriétés améliorées à base de polymères de tétrafluoroéthylène et procédé pour leur préparation - Google Patents

Poudres à fritter fluides à propriétés améliorées à base de polymères de tétrafluoroéthylène et procédé pour leur préparation Download PDF

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Publication number
EP0030664B1
EP0030664B1 EP80107445A EP80107445A EP0030664B1 EP 0030664 B1 EP0030664 B1 EP 0030664B1 EP 80107445 A EP80107445 A EP 80107445A EP 80107445 A EP80107445 A EP 80107445A EP 0030664 B1 EP0030664 B1 EP 0030664B1
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Prior art keywords
weight
polymer
dispersion
polymer powder
filler
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EP0030664A2 (fr
EP0030664A3 (en
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Jürgen Dr. Kuhls
Robert Dr. Hartwimmer
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Hoechst AG
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Hoechst AG
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    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J3/00—Processes of treating or compounding macromolecular substances
    • C08J3/12—Powdering or granulating
    • C08J3/16—Powdering or granulating by coagulating dispersions
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
    • C08F14/00—Homopolymers and copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen
    • C08F14/18—Monomers containing fluorine
    • C08F14/26—Tetrafluoroethene
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
    • C08F259/00—Macromolecular compounds obtained by polymerising monomers on to polymers of halogen containing monomers as defined in group C08F14/00
    • C08F259/08—Macromolecular compounds obtained by polymerising monomers on to polymers of halogen containing monomers as defined in group C08F14/00 on to polymers containing fluorine
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J2327/00—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Derivatives of such polymers
    • C08J2327/02—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Derivatives of such polymers not modified by chemical after-treatment
    • C08J2327/12—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Derivatives of such polymers not modified by chemical after-treatment containing fluorine atoms
    • C08J2327/18—Homopolymers or copolymers of tetrafluoroethylene

Definitions

  • the invention relates to free-flowing sintered powders based on polymers containing at least 98.5% by weight of polymerized tetrafluoroethylene units and a process for their preparation, a colloidal polymer dispersion prepared in the presence of a surface-active compound in an aqueous medium, optionally with the addition of a readily water-soluble, dissociating inorganic compound, stirred until sufficient thickening, indicated by the appearance of clearly visible optical inhomogeneities, then an organic liquid which wets the polymer particles present in the dispersion well, and after a time the polymer granules formed are washed, separated from the aqueous medium and dried .
  • US Pat. No. 2,593,583 discloses a process for producing free-flowing, granulated tetrafluoroethylene polymers, in which a colloidal polymer dispersion prepared in an aqueous medium with the addition of emulsifiers at 0 to 85 ° C. with an energy of about 4 to 200 Js -1 I -1 is stirred without the addition of any aids. Additions of electrolytes or organic precipitants, for example acetone or methanol, are described as disadvantageous.
  • CA-PS 566 352 describes a molding powder which contains a mixture of 80 to 98% by weight (based on the mixture) of carbonyl iron particles and 20 to 2% by weight of tetrafluoroethylene polymer particles with an average particle size of 0.25 contains up to 0.5 ⁇ m.
  • the iron particles are essentially evenly coated with the polymer and can be extruded into self-supporting articles under pressure.
  • the molded powders are produced by adding the iron particles and water to the dispersion with stirring until the desired high content of iron particles is reached and a syrupy liquid is present, which is then stirred vigorously or ground in a ball mill until a dough-like mass is formed. No other additions are made.
  • US Pat. No. 3,046,263 discloses a process for the continuous coagulation of aqueous, colloidal dispersions of tetrafluoroethylene polymers which contain a small proportion of dispersant, in which the dispersion in turn is used briefly, for example in a centrifugal pump with no further additives Energy of approx. 200 to 20,000 Js -1 I -1 mixed in the absence of air, then passed through a capillary tube, which causes a pressure drop of 3.4 to 138 kPa, and then in the presence of air with an energy of 49 to 9850Js -1 I -1 stirred, separated and dried.
  • a method for producing a moldable material for bearings is known, one or more fillers in finely divided form being intimately mixed with the polytetrafluoroethylene-containing dispersion, the dispersion coagulating, the coagulation product being dried, compressed under pressure to a self-supporting solid mass and is then ground.
  • aluminum nitrate or another coagulant is preferably added to the mixture of the filler and the polytetrafluoroethylene dispersion. No other additives are used.
  • DE-AS 1 520 544 describes polytetrafluoroethylene molding powders with a total surface area of at least 3 and less than 9 m 2 / g, a moldability index of less than 50 and a bulk density (apparent density) of 420 to 685 g / l, which preferably have a specific gravity of less than 2.2.
  • the molded powders are produced by a specific polymerization process, in which tetrafluoroethylene is initially polymerized in an aqueous medium at a temperature of 60 to 130 ° C.
  • the aqueous medium having a power consumption in the range from 4 to 20 Js -1 I -1 is stirred at a ratio of power to flow coefficient of at least 1.4 and at least 5.1010 nuclei are formed with a total surface area of more than 9 m 2 / g per ml, after which the polymerization is carried out with particle enlargement until the particles have a total surface area of less than 9 to 3 m 2 / g.
  • the solids are filtered off from the resulting slurry and dispersed in water, cut briefly with a high-speed paddle stirrer and then stirred for a long time just enough to keep the non-water-moist particles % immersed, after which the solids are filtered off and dried. Organic liquids that wet the particles are not added.
  • a method is known, a dry, predominantly polytetrafluoroethylene-containing powder by stirring at temperatures from 0 to 100 ° C in an aqueous emulsion, the 5 to 50 wt .-% organic liquids such as gasoline, benzene, amyl acetate , n-butanol, diisopropyl ether, chloroform or chlorobenzene, to granulate, so that press-sinter powder with a high bulk density of up to over 600 g / 1 is formed.
  • a processed material with a bulk density of 660 g / l is obtained with a starting material with a grain diameter of 0.05 f Lm.
  • the US-PS 39 80 612 describes a similar process in which a powder mixture of a tetrafluoroethylene polymer with a particle size of 5 to 200 microns, which contains 5 to 40 vol .-% of a metal-containing filler, in a two-phase liquid, the Contains water and an organic liquid, with the addition of an aqueous dispersion of a tetrafluoroethylene polymer, which was prepared by polymerization in the presence of an emulsifier, is granulated by stirring.
  • the dry tetrafluoroethylene polymer powder is made by suspension polymerization and follow up of grinding.
  • the granulation mixture contains about 5 to 50 times the amount of dry polymer compared to the polymer added as an aqueous dispersion.
  • DE-AS 2 523 570 discloses a polymerization process in which polymers are obtained with a certain initiator system, including in the presence of an emulsifier, which can be processed by the press-sintering technique without the undesirable crack formation otherwise observed in emulsion polymers To show sinter blocks.
  • the dispersion obtained by emulsion polymerization is diluted by adding water to a solids content of 10% by weight, based on the liquor, and at 22 to 25 ° C. with a stirrer in which 4 four-bladed stirring elements are offset with respect to one another Shaft are distributed, stirred, washed twice and dried. None is said about the use of any additives when stirring the aqueous dispersion.
  • the tetrafluoroethylene-containing polymer and the added filler show a tendency to separate.
  • a special pretreatment of the filler is necessary.
  • the product produced is less suitable for processing in the press-sintering process because of the lack of thermal stability and crack formation in the sintered moldings produced therefrom.
  • “Sinterable polymer powder” in the sense of the present invention is to be understood as meaning polymer powder that has a melt viscosity (shear viscosity) at 350 ° C. of ⁇ 0.1 GPa-s, frequently of ⁇ 1 GPa. s, up to about 900 GPa. have s. Such polymer powders cannot be processed from the melt by customary processing methods for thermoplastics.
  • the melt viscosity (shear viscosity) is measured by the method (creep test) of Ajroldi et al., Described in J. appl. Polym. Sci., 14.1970, page 79 ff. The method is described in more detail in US Pat. No.
  • the sinterable polymer powder preferably consists of primary particles with an average particle size of 0.2 to 0.5 ⁇ m, which are agglomerated into granules with an average grain diameter of preferably 180 to 650 ⁇ m.
  • the polymer is produced by polymerization into colloidal dispersions by the process of emulsion polymerization with or without the use of a seed polymer and, from its production, can also contain residual constituents of polymerization auxiliaries, in particular of a telogenically inactive, fluorinated dispersant. It can be constructed exclusively from polymerized tetrafluoroethylene units or have a uniform modification, such as is obtainable, for example, according to US Pat. No. 3,142,665 or US Pat. No. 3,819,594.
  • the polymer can also have a core / shell structure or a multi-shell structure which is different in terms of the amount and type of modifier, as described by the processes in DE-PS 1 795 078, US-PS 4 036 802, DE-OS 2 620 284 or DE-OS 2 521 738 can be produced.
  • the sinterable polymer powder or the polymer portion of the filler-containing, sinterable polymer powder consists of primary particles, which by polymerization to colloidal dispersions in an aqueous medium in the presence of 0.01 to 0.5 wt .-%, based on the aqueous medium, of at least one telogen inactive fluorinated dispersants have been prepared using the seed technique, 4 to 12, preferably 5 to 10% by weight, based on the end polymer obtained therefrom, of a seed polymer which is composed of 94 to 99.99% by weight polymerized tetrafluoroethylene being used Units and consists of 6 to 0.01 wt .-% polymerized units of a perfluorinated monomer in which a fluorine atom can be replaced by chlorine, the last two wt .-% - refer to the seed polymer.
  • Perfluoroalkenes of the formula are, for example, suitable as perfluorinated monomers in what mean Fluorine or a perfluorinated alkyl radical with 1 to 4, preferably 1 to 2 C atoms, which is straight-chain, and Rf a perfluorinated alkyl radical with 1 to 4, preferably 1 to 2 C atoms, which is straight-chain.
  • Perfluoro (alkyl vinyl) ethers of the formula CF 2 CF-ORf, in which is a perfluorinated alkyl radical having 1 to 5, preferably 1 to 3 carbon atoms, which is straight-chain.
  • perfluorinated dioxanyl vinyl ethers as described in DE-OS 2 544 040, or perfluoropropoxy vinyl ether or perfluoro (2-methylene-4-methyl) 1,3-dioxoian.
  • a fluorine atom can be replaced by a chlorine atom, preferably this chlorine atom is bonded to a carbon atom which carries the double bond.
  • R can also be chlorine or, if R is fluorine, Rf can be chlorine.
  • Perfluoropropyl vinyl ether or perfluoropropylene are particularly preferred as perfluorinated monomers.
  • One or more of the above-mentioned monomers may be present both during the seed polymerization and during the main polymerization carried out in the presence of the seed. Chlorine-containing monomers are expediently only used in seed polymerization. If the polymerization is carried out in different stages, the type and amount of the monomers used can vary from stage to stage.
  • the proportion of perfluorinated monomers which is present during the emulsion polymerization is 0.0005 to 3% by weight, preferably 0.01 to 1.0% by weight, based on the tetrafluoroethylene used, without taking into account a possible seed template, indifferent, whether the emulsion polymerization is carried out with or without presentation of a colloidal seed dispersion.
  • the perfluorinated monomers are preferably metered into the reaction vessel in a total amount before the start of the polymerization. However, they can also be re-introduced into the ongoing polymerization at any time before a conversion of 99.5%, preferably 75%.
  • the main polymerization carried out in the presence of the seed charge can initially only be started with tetrafluoroethylene.
  • the perfluorinated monomers are then fed in at a tetrafluoroethylene conversion of 25 to 99.5%, preferably 75 to 99.5%. Part of the required amount of perfluorinated monomers can also be introduced and a further part can be added during the polymerization. If appropriate, the perfluorinated monomers can be added continuously or in portions from the start of the ongoing polymerization or from reaching the desired degree of conversion.
  • the filler-containing, sinterable polymer powder consists of 95 to 60% by volume, preferably 85 to 70% by volume, of a polymer predominantly containing tetrafluoroethylene units and 5 to 40% by volume, preferably 15 to 30% by volume Filler, the vol .-% - refer to the filler-containing polymer powder.
  • the filler should have a melting point of at least 380 ° C., preferably at least 450 ° C. and should not react with the polymer under processing conditions, that is below 400 to 450 ° C., optionally under a protective gas atmosphere, for example nitrogen.
  • the particle size of the filler should be at most 90% of the particle size of the sinterable, filler-containing polymer powder.
  • the particle size of the filler is limited downwards to an average particle size of 0.1 f Lm due to its manufacturability, tearability and handling.
  • fillers are used microns with a mean particle size of 2 to about 100 f Lm and more particularly with such a from 5 to 60. If it is fibrous products, the particle size information relates to the diameter of the fibers.
  • Suitable fillers are metals and metal alloys, for example iron, copper, silver, bronze, chromium-nickel steel and metal oxides, for example aluminum oxide, titanium oxide, chromium oxide, manganese dioxide, silicon dioxide or metal sulfides, for example molybdenum disulfide, and metal sulfates, for example barium sulfate or metal silicates, for example glass powder or fibers, asbestos, mica, chamotte, ceramic, and also carbon, such as graphite, coal or coke.
  • metals and metal alloys for example iron, copper, silver, bronze, chromium-nickel steel and metal oxides, for example aluminum oxide, titanium oxide, chromium oxide, manganese dioxide, silicon dioxide or metal sulfides, for example molybdenum disulfide, and metal sulfates, for example barium sulfate or metal silicates, for example glass powder or fibers, asbestos, mica, chamotte, ceramic, and also carbon, such as graphit
  • One or more fillers can be used within the volume percentages above.
  • the type, amount added and particle shape of the filler or fillers used influence the density, specific surface area, pourability, bulk density and also the grain stability of the sinterable, filler-containing polymer powder, in some cases considerably, which is why the filler-containing filler produced by the process according to the invention has to be determined to be advantageous Polymer powder can only be compared exactly to those according to the prior art if the same filler or the same filler mixture is used in the same amount.
  • the sinterable, filler-containing polymer powder according to the present invention has a specific surface area of 1.5 to 8, preferably 2 to 7 m 2 / g; a pourability less than 3.1, preferably less than 2.9 s / 25 g; a bulk density of 550 to 1400, preferably 600 to 1400 g / l; a grain stability of 1 to 3.5, preferably 1 to 3.0 s / 50 g; a deformation under load of less than 8%, preferably less than 6% and a ball indentation hardness of greater than 30 N / mm 2 , preferably greater than 35 N / mm 2 to about 45 N / mm 2. These properties are determined by methods, which are given below.
  • the sinterable, non-filler-containing polymer powders according to the present invention have a specific surface area of 5 to 11, preferably 7 to 9 m 2 / g; a standardized specific gravity of less than 2.2, preferably less than 2.17; a pourability less than 3.1, preferably 2.6 s / 25 g; a bulk density of 750 to 860, preferably 750 to 800 g / l; a grain stability of 2.7 to 5, preferably 3 to 4 s / 50 g and a moldability index of less than 11, preferably less than 8.
  • the invention further relates to a process for producing a sinterable, optionally filler-containing polymer powder based on a polymer, which by polymerization in an aqueous medium in the presence of 0.01 to 0.5 wt .-%, based on the aqueous medium, of at least one telogen-inactive, fluorinated dispersant to form a colloidal dispersion with an average particle size of the polymer from 0.05 to 0.8 ⁇ m and a total solids content of 10 to 50 wt.%, based on the dispersion, and which consists of 98 , 5 to 100 wt .-% polymerized tetrafluoroethylene units and 1.5 to 0 wt .-% polymerized units of at least one perfluorinated monomer in which a fluorine atom can be replaced by chlorine and which is copolymerizable with tetrafluoroethylene, wherein the polymer dispersion is adjusted to a solids content of about 5
  • the dispersion is added with 0 to 2 % By weight, based on the dispersion, of at least one water-soluble, dissociating, inorganic salt, which contains an ammonium cation or a metal cation and / or a water-soluble acid with which the pH of the dispersion is adjusted to 0 to 6 until the dispersion has thickened sufficiently, indicated by clearly visible optical inhomogeneities, stirred and 0 to 10 minutes afterwards, without intermediate separation, drying and grinding of the polymer, 1 to 5% by weight, based on the dispersion of an organic liquid which wets the polymer particles in dispersion well and less than 15% by weight in water is soluble at 20 ° C, be added to the dispersion.
  • Polymer dispersions suitable for the process can be prepared by known processes, as described, for example, in US 2,559,752; 3,088,941; 3,142,665; 3,819,594; 4,036,802; DE-OS 1 795 078; 2,521,738 and 2,620,284. It is possible to work without and with the presentation of a seed polymer, in the absence or presence of the perfluorinated monomers described in more detail above, using the polymerization technique which has also already been described.
  • the temperature during the polymerization is generally 10 to 80 ° C, the pressure 0.2 to 3.5 MPa.
  • Dispersions with an average particle size of the polymer of 0.05 to 0.8 ⁇ m are preferably used, further preferred are dispersions which have been prepared in the presence of perfluorinated monomers and whose polymer particles consist of 98.5 to 99.99% by weight of polymerized tetrafluoroethylene -Units and 1.5 to 0.01 wt .-% polymerized units of these perfluorinated monomers exist.
  • Perfluoropropylene or straight-chain perfluoroalkyl vinyl ethers are used in particular as perfluorinated monomers.
  • the dispersion is adjusted, if appropriate with water, to a total solids content of about 5 to 15% by weight, preferably 9 to 11% by weight, provided that it does not come from the polymerization with this solids content and if necessary, brought to a temperature of 10 to about 85 ° C.
  • the process is preferably continued at a temperature of from 15 to 60 ° C., in particular from 15 to 40 ° C.
  • the dispersion is then stirred with an energy of 4 to 200 Js -1 I -1 , preferably at 15 to 70 Js -1 I -1 , until the dispersion has thickened sufficiently, as indicated by the appearance of clearly visible optical inhomogeneities (so-called » Streaks «).
  • stirrers can be used for stirring, for example blade, paddle, propeller, impeller or anchor stirrers or else high-performance stirrers, for example the “Ultra Turrax®” type from Lutz 4 / 22-640.
  • the latter stirrers are preferably only switched on when or after the addition of the organic liquids described in more detail below.
  • baffles can be installed in the agitation vessel.
  • the dispersion may contain up to 2% by weight, preferably 0.01 to 1% by weight, based on the dispersion of at least one water-soluble, dissociating, inorganic salt which contains an ammonium cation or a metal cation and / or a water-soluble acid, with which the pH of the dispersion is adjusted to 0 to 6, are added.
  • Suitable salts are, for example, neutral or acidic salts of sodium, potassium, calcium, magnesium, aluminum of mineral acids, for example hydrochloric acid, sulfuric acid, nitric acid or phosphoric acid.
  • Ammonium salts volatile below 300 ° C., for example ammonium chloride or ammonium nitrate, are preferably used.
  • salts can also be used.
  • one or more water-soluble acids are used, with which the pH of the dispersion is adjusted to 0 to 6, preferably 1 to 4.
  • Strong mineral acids are preferably used for this purpose, the 1 normal aqueous solution of which has a pH of less than 1 at 20 ° C. and which are relatively readily volatile, that is to say which boil or settle as an azeotrope with water at 0.1 MPa below 340 ° C. decompose to form only volatile substances.
  • Examples of such acids are hydrochloric acid, nitric acid and sulfuric acid.
  • the dispersion After the dispersion has thickened sufficiently, as described above, 1 to 5% by weight, preferably 2 to 4% by weight, based on the dispersion, of at least one organic liquid which wets the polymer particles present in the dispersion well and is less than 15% by weight soluble in water at 20 ° C.
  • the stirring is continued in this case, the work is advantageously continued for 1 to 6 minutes and in particular for 2 to 4 minutes with increased stirring energy, for example by switching on a high-performance stirrer, as described above.
  • the previous stirrer can also be switched off and only the high-performance stirrer can be switched on.
  • the increased stirring energy should act so long that rapid and complete granulation of the polymer is achieved. If the intensive stirring is switched on for too long, the granules formed are increasingly comminuted, so that the grain size of the Granules can be adjusted.
  • stirring is continued for about 10 to 100 minutes, preferably 20 to 80 minutes, as described above.
  • the solid is separated from the liquid phase 2 to about 7 times by filtration or sieving and stirred again for washing with water.
  • the solid is finally separated from the liquid phase and dried at temperatures from 100 to 290 ° C., preferably 200 to 280 ° C.
  • a belt dryer or a drying cabinet can be used for this purpose, the drying gas, usually air, being moved, for example by pumping, ventilation or suction.
  • drying is carried out at normal atmospheric pressure. Vacuum can also be used.
  • the organic liquid can be added to the dispersion immediately after the sufficient thickening has been determined or up to 10 minutes afterwards.
  • the organic liquid is preferably added to the dispersion 0 to 3 minutes and in particular 0 to 1 minute after the optical inhomogeneities have occurred.
  • organic liquids examples include: gasoline, n-hexane, n-octane, cyclohexane, benzene, toluene, butyl acetate, amyl acetate, n-butanol, n-hexanol, diethyl ether, diisopropyl ether, chloroform and methylene chloride. Mixtures of several organic liquids can also be added.
  • Organic liquids are advantageously used which are less than 3% by weight soluble in water at 20 ° C., in particular a hydrocarbon or a mixture of hydrocarbons whose boiling point under a pressure of 0.1 MPa at 60 to 180 ° C. preferably at 80 to 150 ° C.
  • the fillers described above are used in the amounts specified there for the production of filler-containing, sinterable polymer powders.
  • the filler or fillers are preferably added together with the addition of the organic liquid or immediately thereafter.
  • the method according to the invention can be used to produce sinterable, optionally filler-containing polymer powders which have a particularly good combination of properties with regard to bulk density, free-flowing properties, grain stability, specific surface area and deformability index with good thermostability.
  • the new process is not very susceptible to faults and can be carried out without major expenditure on equipment and energy.
  • An aluminum cup (height 150 mm; inner diameter: 100 mm) with a flat bottom made of polytetrafluoroethylene is equipped with a three-bladed propeller stirrer (diameter of the Agitator: 96 mm), which is driven by an infinitely variable agitator.
  • the agitator shaft is mounted in the bottom of the cup.
  • the pourability of the polymer powder is determined again. All pourability measurements are carried out with 50 g powder. The difference in free-flowing properties before and after stirring the powder (in s / 50 g) is given as a measure of the grain stability. The smaller this value, the higher the grain stability.
  • circular sintered plates with a diameter of 80 mm and a thickness of 2 mm are used for the determination according to ASTM.
  • Circular plates with a diameter of 45 mm and a thickness of 4 mm are used to measure the polymer powder filled with coal, graphite or bronze.
  • 1 kg of the polymer powder is pressed under a pressure of 25.0 MPa to form a cylindrical block and then sintered for 4 hours at 375 ° C., with subsequent cooling at a rate of 45 ° C./hour.
  • the blocks have a diameter of 95 mm.
  • the sintered 1 kg blocks are peeled down to an inner core with a diameter of 49 mm to form a 200 ⁇ m thick film and the diameter of the unpeeled remaining block is used as a measure of the crack formation when cracks first appear.
  • the tensile strength and elongation at break as well as the dielectric strength are determined on the peeling films obtained, as described below.
  • VDE 0303 / T 2 An insulation tester from Messwandler Bau GmbH, Bamberg; Form IPG 30/05; Electrodes on top 20 mm diameter ball, under 50 mm diameter plate used. The measuring device is modified so that a motor pulls the film by 10 cm after each breakdown, after which a new measurement starts automatically. The voltage required for the breakdown is recorded as a spike using a connected recorder.
  • At least ten individual values are used to calculate an average, whereby values that are below 75% of the second highest value are not used for the calculation.
  • the number of individual values from which the mean value is determined must be at least 70% of the total individual values.
  • the polymer powder to be tested is either used as such or subjected to an annealing at 340 ° C. for 30 minutes. After the tempering, the mean particle size (d 50), the bulk density and the flowability are determined. These powders are made using a RAM extruder with a sintering zone length of 800 mm with the temperature setting in Extru direction: 380, 390, 380 ° C and with an output of 3 m / hour for pipes with an inner diameter of 32 mm and an outer diameter of 39 mm, or with an output of 2 m / hour for rods with a diameter of 22 mm extruded.
  • the tubes are twisted to a wall thickness of 2 mm, test specimens punched out in the direction of extrusion and used in accordance with ASTM 1708 to measure the tensile strength and elongation at break. Platelets with a thickness of 2 mm are milled out of the rods in the direction of extrusion, test specimens are punched out of them and determined according to ASTM 1708 tensile strength and elongation at break.
  • Tear strength and elongation at break are determined according to ASTM-D 1708-66.
  • the test specimens are punched out of pressed plates, the manufacture of which is specified above in the measurement of the standardized specific weight (SSG), but the plates have a thickness of 1.6 mm.
  • cylindrical press-sintered bodies of 45 mm in diameter and 75 mm in height are obtained by pressing at pressures specific to the filler content of the polymer powders from 35 to 70 MPa and sintering at 380 ° C. for 4 hours with a Heating and cooling times of 8 hours each.
  • the determination is made according to ASTM-D 621 at 20 ° C on round test specimens with a diameter of 10 mm and a thickness of 10 mm.
  • the polymer dispersions prepared as described are granulated according to the invention as follows to form polymer powders which do not contain filler:
  • 12 kg of polymer dispersion with a solids content of 20% by weight are added and water with a solids content of 10%. -% diluted.
  • the Ekato stirrer is switched on with a speed of 700 rpm and a stirring energy of 34 Js -1 I -1 , then 30 cm concentrated hydrochloric acid are added. After a short time, clear optical inhomogeneities (so-called streaks) are observed in the dispersion, which indicate sufficient thickening.
  • the amount of petrol from the boiling point range 80 to 110 ° C, given in% by weight, based on the polymer is added and the Ultra Turrax® stirrer is switched on for 3 minutes at a speed of 1. 104 rpm and a stirring energy of 25 Js -1 I -1 .
  • the electric stirrer is further stirred at a speed of 700 rpm for 10 minutes, the granules formed are separated from the liquid phase by boiling, suspended in 20 l of deionized water with stirring and this washing process is repeated five times .
  • the last slurry is stirred for a further 30 minutes as described above, then separated again via sieve granules and water and the granules are dried in a forced-air drying cabinet for 6 hours at 280 ° C. to a polymer powder.
  • Table II The values given in Table II below are measured on this polymer powder obtained by granulation.
  • the sequential number of the respective example is given in the first vertical column of the table, and the polymerization batch according to which the dispersion used was prepared is shown in the second vertical column.
  • the powder properties were measured using the methods described above.
  • the number of revolutions of the stirrer is then increased to 700 rpm and the stirring energy to 34 Js -1 I -1 and 30 cm 3 of concentrated hydrochloric acid are added. After a short time, clear optical inhomogeneities in the dispersion (so-called streaks) are observed, which indicate a sufficient thickening. After a further 2 minutes, the amount (% by weight, based on the polymer) of gasoline from the boiling point range from 80 to 110 ° C. is added and stirring is continued for 60 minutes.
  • the granules formed are then separated from the liquid phase via a sieve, stirred in 20 l of deionized water and this washing process is repeated six times, then the filler-containing granules are dried for 6 hours in a forced-air drying cabinet at 280 ° C. to form a filler-containing, sinterable polymer powder.
  • the values listed in the table below are measured on this polymer powder:
  • non-filler-containing, sinterable polymer powders obtained according to Examples 1 to 9 are, as described above, tested in 1 kg sintered blocks, which are peeled to 200 ⁇ m thick foils, and by RAM extrusion of solid rods and tubes, and in doing so the ones in Table IV below and V measured values determined:
  • test direction is noted in Table V after the elongation at break in brackets.

Claims (13)

1. Poudre de polymère frittable constituée de particules primaires d'une taille de particules moyenne de 0,05 à 0,8 µm, qui sont agglomérées en granulés d'un diamètre de grain moyen de 150 à 850 fLm, le polymère de base contenant 98,5 à 100% en poids d'unités tétrafluoréthylène polymérisées et 1,5 à 0% en poids d'unités polymérisées d'au moins un monomère perfluoré dans lequel un atome de fluor peut être remplacé par du chlore, et qui est copolymérisable avec du tétrafluoréthylène, cette poudre étant caractérisée par une combinaison des propriétés suivantes:
surface spécifique 5 à 11 m 2/g;
poids spécifique standardisé inférieur à 2,2;
fluidité inférieure à 3,1 sec/25 g;
densité apparente 750 à 860 g/I;
stabilité de grain 2,7 à 5 sec/50 g;
indice d'aptitude au moulage inférieur à 11 et
déformation sous charge inférieure à 14%.
2. Poudre de polymère chargée, frittable, constituée de particules primaires d'une taille de particules moyenne de 0,05 à 0,8 [Lm, qui sont agglomérées en granulés d'un diamètre de grain moyen de 500 à 700 µm, ce diamètre de grain moyen des agglomérés devant être d'au moins 35% supérieur au diamètre moyen des particules de la charge, composées de 95 à 60% en volume d'un polymère contenant 98,5 à 100% en poids d'unités tétrafluoréthylène polymérisées et 1,5 à 0% en poids d'unités polymérisées d'au moins un monomère dans lequel un atome de fluor peut être remplacé par du chlore, et qui est copolymérisable avec du tétrafluoréthylène, ainsi que de 5 à 40% en volume d'une charge constituée d'au moins un métal, oxyde, sulfure, silicate, sulfate métallique ou de carbone d'une grosseur de particules représentant au maximum 90% de la grosseur des particules de la poudre de polymère chargée frittable, et d'un point de fusion d'au moins 380°C, tout les pourcentages en volume indiquées se rapportant à la poudre de polymère chargée et tous les pourcentages en poids indiqués se rapportant à la poudre de polymère non chargée, cette poudre de polymère étant caractérisée par la combinaison des caractéristiques suivantes:
surface spécifique 1,5 à 8 m2/g;
fluidité inférieure à 3,1 sec/25 g;
densité apparente 550 à 1400 g/I;
stabilité de grain 1 à 3,5 sec/50 g;
déformation sous charge inférieure à 8% et
dureté à la bille supérieure à 30 N/mm2.
3. Poudre de polymère frittable selon la revendication 1, caractérisée par le fait qu'elle présente un poids spécifique standardisé inférieur à 2,17 g/cm3.
4. Poudre de polymère frittable selon la revendication 1, caractérisée par le fait qu'elle présente un indice d'aptitude au moulage inférieur à 8.
5. Poudre de polymère frittable selon la revendication 2, caractérisée par le fait qu'elle présente une déformation sous charge inférieure à 6%.
6. Poudre de polymère frittable selon les revendications 1 à 5, caractérisée par le fait que la proportion de polymère est préparée par polymérisation en milieu aqueux, selon la technique de semence, en présence de 0,01 à 0,5% en poids, rapporté au milieu aqueux, d'au moins un dispersant fluoré télogéniquement inactif, avec utilisation de 4 à 12% en poids, rapporté au polymère final résultant, d'un polymérisat de semence composé de 94 à 99,99% en poids d'unités tétrafluoréthylène et 6 à 0,01 % en poids d'unités polymérisées d'un monomère perfluoré dans lequel un atome de fluor peut être remplacé par du chlore, les deux derniers pourcentages en poids se rapportant au polymérisat de semence.
7. Poudre de polymère frittable selon les revendications 1 à 6, dont la proportion de polymère est composée de 98,5 à 99,99% en poids d'unités tétrafluoréthylène polymérisées et 1,5 à 0,01% en poids d'unités polymérisées d'au moins un monomère perfluoré à chaîne ouverte qui contient un groupe CF2=C, 3 à 6 atomes de carbone et 0 à 2 atomes d'oxygène.
8. Poudre de polymère frittable selon la revendication 7, caractérisée par le fait que le monomère perfluoré est un éther perfluoralkyl-vinylique à chîne droite.
9. Poudre de polymère frittable selon la revendication 7, caractérisée par le fait que le monomère perfluoré est du perfluoropropylène.
10. Procédé de préparation d'une poudre de polymère frittable, éventuellement chargée, à base d'un polymère composé de 98,5 à 100% en poids d'unités tétrafluoréthylène polymérisées et 1,5 à 0% en poids d'unités polymérisées d'au moins un monomère perfluoré dans lequel un atome de fluor peut être remplacé par du chlore, et qui est copolymérisable avec du tétrafluoréthylène, selon l'une des revendications 1 ou 2, ledit polymère étant préparé par polymérisation en milieu aqueux, en présence de 0,01 à 0,5% en poids, rapporté au milieu aqueux, d'au moins un dispersant fluoré télogéniquement inactif, avec formation d'une dispersion colloidale d'une grosseur moyenne des particules du polymère de 0,05 à 0,8 µm et d'une teneur totale en solides de 10 à 50% en poids, rapporté à la dispersion, la dispersion de polymère étant réglée à une teneur en solides d'environ 5 à 15% en poids et étant brassée entre 10 et 85°C avec une énergie de 4 à 200 Js-1I-1, avec addition d'un liquide organique, après quoi on ajoute éventuellement la charge et, après formation des granulés, on lave, on sépare définitivement de la phase liquide et on sèche, ce procédé étant caractérisé par le fait qu'avant l'addition du liquide organique on brasse la dispersion avec addition de 0 à 2% en poids, rapporté à la dispersion, d'au moins un sel inorganique soluble dans l'eau, à effet dissociant, qui contient un cation ammonium ou un cation métallique, et/ou d'un acide soluble dans l'eau avec lequel le pH de la dispersion est réglé à 0-6, jusqu'à épaississement suffisant de la dispersion indiquée par les non-homogénéités optiques nettement perceptibles, et, 0 à 10 minutes après, sans séparation, séchage et broyage du polymère, on ajoute à la dispersion 1 à 5% en poids, rapporté à la dispersion, d'un liquide organique mouillant convenablement les particules de polymère contenues dans la dispersion et qui est soluble à moins de 15% en poids dans l'eau à 20°C.
11. Procédé selon la revendication 10, caractérisé par le fait qu'on ajoute 0,01 à 1 % en poids, rapporté à la dispersion, d'un sel soluble dans l'eau ou d'un acide.
12. Procédé selon les revendications 10 et 11, caractérisé par le fait qu'on opère à une température de 15 à 60°C.
13. Procédé selon les revendications 10 à 12, caractérisé par le fait que le liquide organique est ajouté à 0 à 3 minutes après l'apparition des non-homogénéités optiques, en particulier 0 à 1 minutes après.
EP80107445A 1979-12-12 1980-11-28 Poudres à fritter fluides à propriétés améliorées à base de polymères de tétrafluoroéthylène et procédé pour leur préparation Expired EP0030664B1 (fr)

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DE19792949908 DE2949908A1 (de) 1979-12-12 1979-12-12 Rieselfaehige sinterpulver mit verbesserten eigenschaften auf basis von tetrafluorethylen-polymeren und verfahren zu deren herstellung

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DE3069917D1 (en) 1985-02-14
ES497511A0 (es) 1981-10-16
US4368296A (en) 1983-01-11
JPS56131629A (en) 1981-10-15
JPH0217576B2 (fr) 1990-04-20
EP0030664A2 (fr) 1981-06-24
US4408007A (en) 1983-10-04
DE2949908A1 (de) 1981-06-19
EP0030664A3 (en) 1981-09-30
ZA807757B (en) 1982-01-27
CA1192348A (fr) 1985-08-20
ES8107275A1 (es) 1981-10-16

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